1. Field of the Invention
The present invention relates to an in-vivo imaging system and a body-insertable apparatus.
2. Description of the Related Art
Of apparatuses that are conventionally used to observe inside human or animal subjects, there are endoscopes having two ends with one end thereof being inserted into the subject to observe inside the subject (hereinafter, simply referred to as an “endoscope”) and capsule-shaped endoscopes (hereinafter, simply referred to as a “capsule endoscope”). Examples of endoscopes include electronic endoscopes that have, for example, a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) at the distal end thereof and also include fiberscopes having a tube probe through which a bundle of optical fibers is inserted. With such an endoscope, images of the inside of the subject are acquired by inserting the probe through, for example, the mouth or the anus of the subject (see, for example, Japanese Patent No. 3898781).
In contrast, a capsule endoscope is a capsule-shaped body-insertable apparatus that is inserted into the subject, and whose size is such that it can be swallowed by humans or animals. Such a capsule endoscope is inserted, for example, orally into the subject. The capsule endoscope that is inserted into the subject captures, for example, periodically, an image inside the subject and sends, to an external receiving device, the captured image from inside the subject as a wireless signal (see, for example, Japanese Laid-open Patent Publication No. 2003-70728). An observer replays, one by one or continuously, multiple images obtained using the endoscope or the capsule endoscope and observes the images, thereby observing inside the subject.
In endoscopes, white light sources, such as halogen lamps, are used for light sources for illuminating inside the subject. Furthermore, in endoscopes, an image-capturing mechanism that uses a frame sequential color filter method is used and in which a monochrome CCD and rotating color filters are used for the image-capturing mechanism. White light sources, such as halogen lamps can generally emit, in a visible light band, light of substantially uniform intensity. With the image-capturing mechanism using the frame sequential color filter method, by conforming to the transmittances of the light of each filter for the three primary colors (R, G, and B), it is possible to easily obtain a uniform light receiving sensitivity for each color component. Accordingly, by using a white light source and an image-capturing mechanism that uses the frame sequential color filter method, it is possible to obtain a clear and well-balanced image for each color component.
However, white light sources, such as halogen lamps, and an image-capturing mechanism using the frame sequential color filter method have a relatively large structure and also require a relatively large amount of electrical power. Accordingly, it is difficult to install, in a capsule endoscope having a size limit, the white light source and the image-capturing mechanism described above. Therefore, with conventional capsule endoscopes, light emitting diodes (LED) that are relatively small in size and whose electrical power consumption is relatively small are used as light sources. Furthermore, with conventional capsule endoscopes, CCD arrays that include a receiving element for each of the three primary colors are used as imaging units.
Japanese Laid-open Patent Publication No. 2002-369217 discloses a technology in which, when an LED and a CCD array are used, by positioning the center wavelength of an emission spectrum of the LED between the main spectral sensitivities of each CCD, the color or luminance of the captured image are brought closer to the original color of the object.
However, in recent years, due to the diversification of observation, required capsule endoscopes are those capable of acquiring, in addition to an image obtained when the image is captured using a white light (hereinafter, referred to as a “normal-light image” or a “white light image”), an image obtained when the image is irradiated with light having a certain wavelength (hereinafter, referred to as a “special light”) (hereinafter, referred to as a “special-light image”).
Accordingly, in recent years, there have been capsule endoscopes in which color filters are arranged in light-receiving units, such as CCDs. However, with such capsule endoscopes, each light-receiving unit for RGB color components has an arch-shaped receiving wavelength spectrum. Accordingly, if light having a flat-shaped emission wavelength spectrum is incident, for each color component, on the light-receiving unit having the arch-shaped receiving wavelength spectrum, there may be a case in which receiving wavelength spectra that are combined (a combined receiving wavelength spectrum) are not flat-shaped spectra. As a result, in some cases, a normal-light image obtained using the capsule endoscope may not be an image that is accurately captured.
Furthermore, when using the technology disclosed in, for example, Japanese Laid-open Patent Publication No. 2005-74034, although a normal-light image can be obtained, in order to obtain a special-light image, a process is required, for example, in which a specific wavelength component is extracted from the normal-light image. This increases the burden imposed on the image processing. Furthermore, in Japanese Laid-open Patent Publication No. 2005-74034 described above, because special-light images are not considered, it is not possible to obtain, except for normal-light images, the special-light images.